JSM Show Post Metadata < 4.9.1 - Contributor+ Stored XSS via Custom Field Meta Key

The JSM Show Post Metadata WordPress plugin before 4.9.1 does not properly escape a post meta key before outputting it into an inline event-handler attribute in an admin-facing meta box, allowing users with contributor-level access and above to inject arbitrary JavaScript that executes in the session of a higher-privileged user who reviews the affected post.